Centrifugal compressor

ABSTRACT

A centrifugal compressor is provided with a ring member including a circumferential wall, a high-speed shaft located at an inner side of the circumferential wall, and rollers located between the circumferential wall and the high-speed shaft. Each roller includes a circumferential surface and first and second end surfaces. The circumferential surface of each of the rollers includes a contact surface that contacts a portion in a circumferential surface of the high-speed shaft, a first non-contact surface spaced apart from the circumferential surface of the high-speed shaft, and a second non-contact surface spaced apart from the circumferential surface of the high-speed shaft. The contact surface includes a center position located closer to the first flange than a center position of each of the rollers in an axial direction of the rollers.

BACKGROUND ART

The present invention relates to a centrifugal compressor.

Japanese Laid-Open Patent Publication No. 2016-194251 describes an example of a centrifugal compressor including a speed increaser. One example of a centrifugal compressor includes an impeller housing that accommodates an impeller and a speed increaser housing that accommodates a speed increasing mechanism. The speed increasing mechanism includes a ring member, a high-speed shaft, and rollers. The rotation of a low-speed shaft rotates the ring member. The high-speed shaft is located at the inner side of the ring member. The rollers are located between the ring member and the high-speed shaft in contact with both of the ring member and the high-speed shaft. The high-speed shaft includes a portion that is inserted into the impeller housing and integrated with the impeller. The speed increasing mechanism is supplied with oil for lubrication.

When the high-speed shaft tilts, the impeller may come into contact with an inner surface of the impeller housing. Thus, in a centrifugal compressor that includes a speed increaser, it is desirable that the high-speed shaft be stably supported.

SUMMARY

It is an object of the present invention to provide a centrifugal compressor that stably supports the high-speed shaft.

A centrifugal compressor that solves the above problem is provided with a ring member, a high-speed shaft, a plurality of rollers, an impeller, a speed increaser housing member, and an impeller housing member. The ring member includes a circumferential wall and is configured to rotate when a low-speed shaft rotates. The high-speed shaft is located at an inner side of the circumferential wall. The rollers are located between the circumferential wall and the high-speed shaft. The rollers are configured to contact the circumferential wall and the high-speed shaft by means of oil. The impeller is configured to rotate integrally with the high-speed shaft. The speed increaser housing member accommodates the ring member, the rollers, and part of the high-speed shaft. The impeller housing member accommodates the impeller. The rollers each include a circumferential surface, a first end surface, and a second end surface. The first end surface and the second end surface are defined by two end surfaces in an axial direction of the roller. The high-speed shaft includes a first flange and a second flange. The first flange is opposed to the first end surface of each of the rollers. The second flange is opposed to the second end surface of each of the rollers and located farther from the impeller than the first flange in the axial direction of the high-speed shaft. The circumferential surface of each of the rollers includes a contact surface, a first non-contact surface, and a second non-contact surface. The contact surface contacts a portion in a circumferential surface of the high-speed shaft between the first flange and the second flange. The first non-contact surface defined by a portion of the circumferential surface extending from an edge of the contact surface to the first end surface and spaced apart from the circumferential surface of the high-speed shaft. The second non-contact surface defined by a portion of the circumferential surface extending from an edge of the contact surface to the second end surface and spaced apart from the circumferential surface of the high-speed shaft. The contact surface includes a center position located closer to the first flange than a center position of each of the rollers in an axial direction of each of the rollers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view showing one embodiment of a centrifugal compressor;

FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1 showing a portion of a speed increaser in the centrifugal compressor of FIG. 1;

FIG. 3 is a perspective view showing the relationship of rollers and a high-speed shaft in the centrifugal compressor of FIG. 1;

FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 2 showing a portion of the speed increaser in the centrifugal compressor of FIG. 1;

FIG. 5 is a cross-sectional view showing rollers in a comparative example;

FIG. 6 is a cross-sectional view showing a modified example of the speed increasing mechanism; and

FIG. 7 is a cross-sectional view showing a further modified example of the speed increasing mechanism.

DETAILED DESCRIPTION OF THE EMBODIMENTS

One embodiment of a centrifugal compressor will now be described. The centrifugal compressor is installed in a fuel cell vehicle (FCV) that is powered by a fuel cell. The centrifugal compressor supplies the fuel cell with air.

As shown in FIG. 1, a centrifugal compressor 10 includes a low-speed shaft 11, a high-speed shaft 12, an electric motor 13 that rotates the low-speed shaft 11, a speed increaser 60, and an impeller 52. The speed increaser 60 increases the rotation speed of the low-speed shaft 11 and transmits the rotation to the high-speed shaft 12. The impeller 52 is rotated by the high-speed shaft 12 to compress fluid (air in the present embodiment).

The high-speed shaft 12 includes a cylindrical shaft body 14, a first flange 15, and a second flange 16. The first flange 15 and the second flange 16 are both annular and extend in the radial direction from the shaft body 14. The first flange 15 and the second flange 16 are spaced apart from each other in the axial direction of the high-speed shaft 12. The shaft body 14 includes a supported portion 17 and a projected portion 18. The supported portion 17 is the portion between the first flange 15 and the second flange 16. The projected portion 18 extends from the first flange 15 opposite to the supported portion 17 in the axial direction. The second flange 16 is arranged on the one of the two axial ends of the high-speed shaft 12 that is farther from the impeller 52. The first flange 15 is located closer to the impeller 52 than the second flange 16 in the axial direction of the high-speed shaft 12. The two shafts 11 and 12 are formed from, for example, a metal, more specifically, iron or an iron alloy.

The centrifugal compressor 10 includes a housing 20 that forms the outer shell of the centrifugal compressor 10. The housing 20 accommodates the two shafts 11 and 12, the electric motor 13, and a speed increasing mechanism 61 that forms part of the speed increaser 60. The housing 20 is, for example, substantially tubular (specifically, cylindrical) as a whole. The two axial ends of the housing 20 define a first end surface 20 a and a second end surface 20 b.

The housing 20 includes a motor housing member 21 that accommodates the electric motor 13, a speed increaser housing member 23 that accommodates the speed increasing mechanism 61, and an impeller housing member 50 including a suction port 50 a that draws in fluid. The suction port 50 a is located in the first end surface 20 a of the housing 20. The impeller housing member 50, the speed increaser housing member 23, and the motor housing member 21 are aligned in this order from the side closer to the suction port 50 a in the axial direction of the housing 20. In the present embodiment, the speed increasing mechanism 61 and the speed increaser housing member 23 form the speed increaser 60.

The motor housing member 21 is tubular (specifically, cylindrical) as a whole and includes a closed end 22 (end wall). The second end surface 20 b defines the outer surface of the closed end 22 of the motor housing member 21 and is located at the side of the housing 20 opposite to the first end surface 20 a, which includes the suction port 50 a. The speed increaser housing member 23 includes a main body 25 and a cover 26. The main body 25 is tubular (specifically, cylindrical) and includes a closed end 24 (end wall). The cover 26 is located at the side opposite to the closed end 24 in the axial direction of the main body 25.

The motor housing member 21 and the speed increaser housing member 23 are coupled to each other with the open end of the motor housing member 21 joined with the closed end 24 of the main body 25. The closed end 24 has an end surface 24 a covered by the motor housing member 21. The inner surface of the motor housing member 21 and the end surface 24 a define a motor accommodation chamber S1. The motor accommodation chamber S1 accommodates the electric motor 13. Further, the motor accommodation chamber S1 accommodates the low-speed shaft 11 in a state in which the low-speed shaft 11 is coaxial with the housing 20.

The low-speed shaft 11 is supported by the housing 20 in a rotatable manner. The centrifugal compressor 10 includes a first bearing 31. The first bearing 31 is arranged in the closed end 22 of the motor housing member 21. The low-speed shaft 11 includes a first end 11 a supported by the first bearing 31. Part of the first end 11 a is inserted through the first bearing 31 and fitted into the closed end 22 of the motor housing member 21.

The closed end 24 of the main body 25 includes an insertion hole 27 that is slightly larger than a second end 11 b of the low-speed shaft 11 located at the side opposite to the first end 11 a. The centrifugal compressor 10 includes a second bearing 32, which is located in the insertion hole 27, and a seal 33. The second end 11 b of the low-speed shaft 11 is supported by the second bearing 32. The seal 33 restricts the leakage of oil O from the speed increaser housing member 23 to the motor accommodation chamber S1.

The second end 11 b of the low-speed shaft 11 is inserted into the insertion hole 27 of the main body 25. Part of the low-speed shaft 11 is located in the speed increaser housing member 23.

The electric motor 13 includes a rotor 41 that is fixed to the low-speed shaft 11 and a stator 42 that is located at the radially outer side of the rotor 41. The stator 42 is fixed to the inner surface of the motor housing member 21. The stator 42 includes a cylindrical stator core 43 and a coil 44 wound around the stator core 43. The rotor 41 and the low-speed shaft 11 rotate integrally when current flows to the coil 44.

The cover 26 is disk-shaped and has the same diameter as the speed increaser housing member 23. The two sides of the cover 26 in the axial direction respectively define first and second plate surfaces 26 a and 26 b. The speed increaser housing member 23 is assembled by joining the open end of the main body 25 with the first plate surface 26 a. The first plate surface 26 a of the cover 26 and the inner surface of the speed increaser housing member 23 define a speed increaser chamber S2. The speed increaser chamber S2 accommodates the speed increasing mechanism 61.

The cover 26, which is one element of the speed increaser housing member 23, includes a cover insertion hole 28 that allows for insertion of the high-speed shaft 12, which forms part of the speed increasing mechanism 61. The projected portion 18 of the high-speed shaft 12 is inserted through the insertion hole 28 and projected out of the speed increaser chamber S2. The first flange 15, the second flange 16, and the supported portion 17 are located in the speed increaser chamber S2. The centrifugal compressor 10 includes a seal 34 located between the high-speed shaft 12 and the wall surface of the cover insertion hole 28. The seal 34 restricts the leakage of the oil O from the speed increaser housing member 23 to the impeller housing member 50.

The impeller housing member 50 is substantially tubular and includes a through hole 51 that extends through the impeller housing member 50 in the axial direction. The two axial ends of the impeller housing member 50 respectively define a first end surface 50 b and a second end surface 50 c. The first end surface 50 b of the impeller housing member 50 defines the first end surface 20 a of the housing 20. The through hole 51 opens in the first end surface 50 b and functions as the suction port 50 a.

The impeller housing member 50 and the cover 26 are coupled to each other with the second end surface 50 c joined with the second plate surface 26 b. The second end surface 50 c is the end surface of the impeller housing member 50 at the side opposite to the first end surface 50 b, and the second plate surface 26 b is the end surface of the cover 26 at the side opposite to the first plate surface 26 a. The wall surface of the through hole 51 and the second plate surface 26 b of the cover 26 define an impeller chamber S3. The impeller chamber S3 accommodates the impeller 52. The through hole 51 functions as the suction port 50 a and defines the impeller chamber S3. The suction port 50 a is in communication with the impeller chamber S3. The cover 26, which is located between the speed increaser chamber S2 and the impeller chamber S3, functions as a partition that separates the speed increaser chamber S2 and the impeller chamber S3.

The through hole 51 has a diameter that is constant from the suction port 50 a to an intermediate position in the axial direction. The through hole 51 from the intermediate position has the form of a substantially truncated cone of which the diameter gradually increases toward the cover 26. Thus, the impeller chamber S3 defined by the wall surface of the through hole 51 substantially has the form of a truncated cone.

The impeller 52 has a contour that is gradually reduced in diameter from the basal end surface 52 a toward the distal end surface 52 b. The impeller 52 includes a shaft insertion hole 52 c that extends in the axial direction of the impeller 52 and allows for insertion of the high-speed shaft 12.

The impeller 52 is coupled to the high-speed shaft 12 with the projected portion 18 of the high-speed shaft 12 inserted through the shaft insertion hole 52 c. The impeller 52 is rotated integrally with the high-speed shaft 12.

A back surface region S4 is defined between the basal end surface 52 a of the impeller 52 and the second plate surface 26 b of the cover 26. The rotation of the high-speed shaft 12 rotates the impeller 52 and compresses the fluid drawn through the suction port 50 a.

Further, the centrifugal compressor 10 includes a diffuser passage 53 and a discharge chamber 54. The fluid compressed by the impeller 52 flows into the diffuser passage 53. The fluid that passes through the diffuser passage 53 enters the discharge chamber 54. The through hole 51 includes an open end that opens toward the second plate surface 26 b of the cover 26 and is continuous with the diffuser passage 53. The diffuser passage 53 is defined by the second plate surface 26 b and the surface of the impeller housing member 50 opposing the second plate surface 26 b. The diffuser passage 53 is located outward from the impeller chamber S3 in the radial direction of the high-speed shaft 12 and has a closed shape (specifically, circular shape) so as to surround the impeller 52 and the impeller chamber S3. The discharge chamber 54 has a closed shape and is located outward from the diffuser passage 53 in the radial direction of the high-speed shaft 12. The impeller chamber S3 is in communication with the discharge chamber 54 through the diffuser passage 53. The fluid compressed by the impeller 52 is further compressed in the diffuser passage 53 and then discharged out of the discharge chamber 54.

The speed increaser 60 will now be described. The speed increaser 60 of the present embodiment is of a traction drive type (friction roller type).

As shown in FIGS. 1 and 2, the speed increasing mechanism 61 of the speed increaser 60 includes a ring member 62 that is coupled to the second end 11 b of the low-speed shaft 11. The ring member 62 includes a disk-shaped base 63 and a circumferential wall 64. The base 63 is coupled to the second end 11 b of the low-speed shaft 11, and the circumferential wall 64 is ring-shaped and extends from the circumferential edge of the base 63. The circumferential wall 64 has an inner diameter that is larger than the diameter of the second end 11 b of the low-speed shaft 11.

In the present embodiment, the ring member 62 is coupled to the low-speed shaft 11 in a state in which the base 63 (ring member 62) is coaxial with the low-speed shaft 11. The circumferential wall 64 is also coaxial with the low-speed shaft 11. The rotation of the low-speed shaft 11 rotates the ring member 62.

Part of the high-speed shaft 12 is located at the inner side of the circumferential wall 64 in the radial direction of the ring member 62. The speed increasing mechanism 61 include three rollers 71 located between the high-speed shaft 12 and the circumferential wall 64 in contact with both of the circumferential wall 64 and the high-speed shaft 12.

As shown in FIGS. 3 and 4, the three rollers 71 are identically shaped. The rollers 71 each include a cylindrical roller portion 72, first and second end surfaces 72 a and 72 b in the axial direction of the roller portion 72, a cylindrical first projection 73 that projects from the first end surface 72 a, and a cylindrical second projection 74 that projects from the second end surface 72 b. The first end surface 72 a and the second end surface 72 b of the roller portion 72 are defined by the two axial end surfaces of each roller 71.

The first projection 73 and the second projection 74 have the same axial dimensions. The roller portion 72 is coaxial with the first projection 73 and the second projection 74. The axial direction of the roller portion 72 will hereinafter be referred to as the axial direction Z of the rollers 71.

The roller portion 72 includes a cylindrical contact region 75, a first non-contact region 76 that is gradually reduced in diameter from the contact region 75 toward the first end surface 72 a, and a second non-contact region 77 that is gradually reduced in diameter from the contact region 75 toward the second end surface 72 b. The contact region 75 is set to be larger in diameter (length in direction orthogonal to axial direction Z) than the supported portion 17 of the high-speed shaft 12. The first end surface 72 a is the end surface of the first non-contact region 76 in the axial direction Z. The second end surface 72 b is the end surface of the second non-contact region 77 in the axial direction Z. The distance between the first end surface 72 a and the second end surface 72 b in the axial direction Z is slightly shorter than axial dimension of the supported portion 17.

The circumferential surface of the roller portion 72 includes a contact surface A, a first non-contact surface B1, and a second non-contact surface B2. The contact surface A is defined by the circumferential surface of the contact region 75, the first non-contact surface B1 is defined by the circumferential surface of the first non-contact region 76, and the second non-contact surface B2 is defined by the circumferential surface of the second non-contact region 77.

The contact surface A includes a first edge and a second edge in the axial direction Z. The first edge is located at the side of the first end surface 72 a. The second edge is located at the side of the second end surface 72 b. The first non-contact surface B1 extends from the first edge of the contact surface A to the first end surface 72 a. The first non-contact surface B1 is a curved surface having an arcuate cross section bulged outward in the radial direction. The second non-contact surface B2 extends from the second edge of the contact surface A to the second end surface 72 b. The second non-contact surface B2 is a curved surface having an arcuate cross section bulged outward in the radial direction.

The first non-contact surface B1 has a shorter dimension in the axial direction Z than the second non-contact surface B2. Thus, the center position CP1 of the contact surface A in the axial direction Z is closer to the first end surface 72 a than the center position CP2 of the roller 71 in the axial direction Z. In other words, in the axial direction Z, the center position CP1 of the contact surface A is located between the center position CP2 of the roller 71 and the first end surface 72 a. The center position CP2 of the roller 71 in the axial direction Z refers to a middle position between the first end surface 72 a and the second end surface 72 b in the axial direction Z. That is, the center position CP2 of the roller 71 in the axial direction Z refers to the center position CP2 of the roller portion 72 in the axial direction Z.

The radial dimension of each roller 71 from the boundary P1 of the first non-contact surface B1 and the contact surface A to the boundary P2 of the first non-contact surface B1 and the first end surface 72 a is referred to as the first dimension L1. The first dimension L1 is also the radial dimension of the roller 71 from the contact surface A to the boundary P2 of the first non-contact surface B1 and the first end surface 72 a. The radial dimension of the roller 71 from the contact surface A to the boundary P4 of the second non-contact surface B2 and the second end surface 72 b is referred to as the second dimension L2. The second dimension L2 is also the radial dimension of the roller 71 from the boundary P3 of the second non-contact surface B2 and the contact surface A to the boundary P4 of the second non-contact surface B2 and the second end surface 72 b. The second dimension L2 is longer than the first dimension L1. In other words, the diameter of the second end surface 72 b, which is the minimum diameter of the second non-contact region 77, is smaller than the diameter of the first end surface 72 a, (which is the minimum diameter of the first non-contact region 76. The rollers 71 are each formed from, for example, a metal. More specifically, the rollers 71 are formed from the same metal as the high-speed shaft 12, for example, iron or an iron alloy.

The axial direction Z of the roller portion 72 coincides with the axial direction of the high-speed shaft 12. The rollers 71 are arranged in the circumferential direction of the high-speed shaft 12 spaced apart from one another.

The rollers 71 are arranged so that each roller portion 72 is located between the first flange 15 and the second flange 16. The roller portion 72 is arranged so that the first end surface 72 a is opposed to the first flange 15 and the second end surface 72 b is opposed to the second flange 16. The first non-contact surface B1 is arranged at the side of the contact surface A where the first flange 15 is located, and the second non-contact surface B2 is located at the side of the contact surface A where the second flange 16 is located. The center position CP1 of the contact surface A in the axial direction Z is closer to the first flange 15 than the center position CP2 of the roller 71 (the roller portion 72) in the axial direction Z. In other words, in the axial direction Z, the center position CP1 of the contact surface A is located between the center position CP2 of the roller 71 (roller portion 72) and the first flange 15.

The first non-contact surface B1 is spaced apart from the circumferential surface of the supported portion 17 so that a region surrounded by the circumferential surface of the supported portion 17, the first non-contact surface B1, and the first flange 15 defines a first gap C1. The second non-contact surface B2 is spaced apart from the circumferential surface of the supported portion 17 so that a region surrounded by the circumferential surface of the supported portion 17, the second non-contact surface B2, and the second flange 16 defines a second gap C2. The first gap C1 is defined between the first non-contact surface B1 and the circumferential surface of the high-speed shaft 12, and the second gap C2 is defined between the second non-contact surface B2 and the circumferential surface of the high-speed shaft 12. The second gap C2 is larger than the first gap C1.

The non-contact surfaces B1 and B2 reduce the area of contact between the circumferential surface of the roller portion 72 and the circumferential surface of the supported portion 17 as compared with when the entire circumferential surface of the roller portion 72 contacts the circumferential surface of the supported portion 17. Thus, the surface pressure that the roller portion 72 applies to the supported portion 17 is increased as compared with when the entire circumferential surface of the roller portion 72 contacts the circumferential surface of the supported portion 17.

When the dimension of the contact surface A in the axial direction Z is too short, the surface pressure will be raised in excess and cause plastic deformation of the high-speed shaft 12. More specifically, the area of contact easily increases and raises the surface pressure at the high-speed shaft 12 including the circumferential surface that contacts the rollers 71 as compared with the circumferential wall 64 including the inner circumferential surface that contacts the outer circumferential surfaces of the rollers 71. Thus, when the dimension of the contact surface A in the axial direction Z is overly reduced, the surface pressure will be raised in excess and cause plastic deformation.

Further, there are many factors that result in the tilting of the high-speed shaft 12 in the centrifugal compressor 10 such as the high-speed shaft 12 being supported by the holding force of the rollers 71 instead of a bearing or slight dimensional differences resulting from the manufacturing tolerance of the rollers 71. Thus, when the area of contact between the rollers 71 and the circumferential surface of the high-speed shaft 12 is reduced too much, the high-speed shaft 12 may not be stably supported when the impeller 52 rotates.

Accordingly, it is desirable that the dimension of the contact surface A in the axial direction Z be, for example, 30% to 90% of the dimension of the supported portion 17 in the axial direction Z.

As shown in FIGS. 1 and 2, the speed increasing mechanism 61 includes a support 80. The support 80 cooperates with the cover 26 to support the rollers 71 so that the rollers 71 are rotatable. The support 80 is located at the inner side the circumferential wall 64. The support 80 includes a disk-shaped support base 81 that is slightly smaller in diameter than the circumferential wall 64 and three posts 82 that extend in the axial direction from the support base 81. The support base 81 is opposed to the cover 26 in the axial direction Z. The support base 81 includes an opposing plate surface 81 a that is opposed to the first plate surface 26 a of the cover 26. The three posts 82 extend from the opposing plate surface 81 a toward the cover 26 filling three gaps that are each defined between the circumferential wall 64 and two adjacent ones of the roller portions 72.

As shown in FIGS. 1 and 2, the support 80 includes the three posts 82. The posts 82 each include a bolt hole 84 that allows for insertion of a bolt 83 extending in the axial direction Z. The cover 26 includes threaded holes 85 corresponding to the bolt holes 84. Each bolt hole 84 is in communication with the corresponding threaded hole 85. In a state in which the distal end surfaces of the posts 82 are joined with the first plate surface 26 a, the posts 82 are fixed to the cover 26 by inserting each bolt 83 through the corresponding bolt hole 84 and fastening the bolt 83 to the corresponding threaded hole 85.

The speed increaser 60 includes first roller bearings 78 and second roller bearings 79 that support the rollers 71 in a rotatable manner. The first roller bearings 78 and the second roller bearings 79 may be bearings other that roller bearings such as, for example, plain bearings. The first roller bearings 78 are arranged in the cover 26. The second roller bearings 79 are arranged in the support base 81. The rollers 71 are supported by the first roller bearings 78 and the second roller bearings 79 so as to be held between the cover 26 and the support base 81.

As shown in FIG. 2, the rollers 71, the ring member 62, and the high-speed shaft 12 form a unit with each roller portion 72 forced against the high-speed shaft 12 and the circumferential wall 64. The high-speed shaft 12 is supported by the three roller portions 72 in a rotatable manner. The location where the outer circumferential surface of each roller portion 72 contacts the inner circumferential surface of the circumferential wall 64 is referred to as the ring contact location Pa, and the location where the outer circumferential surface of each roller portion 72 contacts the circumferential surface of the high-speed shaft 12 is referred to as the shaft contact location Pb. A pressing load is applied to the ring contact locations Pa and the shaft contact locations Pb. The contact locations Pa and Pb each extend in the axial direction Z.

As shown in FIG. 1, the centrifugal compressor 10 includes an oil supplying mechanism 100 that supplies the oil O to the speed increasing mechanism 61. The oil supplying mechanism 100 includes a pump 101 and an oil passage 102. The pump 101 is driven so that the oil O circulates through the oil passage 102 and flows to the speed increaser chamber S2.

The pump 101 is arranged in the closed end 22 of the motor housing member 21. The pump 101 of the present embodiment is of a displacement type. The pump 101 includes an accommodation portion 103, which is located in the closed end 22, and a rotation body 104. The first end 11 a of the low-speed shaft 11 is coupled to the rotation body 104.

The housing 20 includes a supply conduit 105, which forms part of the oil passage 102, and a circulation conduit 106, which forms part of the oil passage 102. The supply conduit 105 connects the accommodation portion 103 and the inside of the ring member 62. The circulation conduit 106 connects the speed increaser chamber S2 and the accommodation portion 103. The centrifugal compressor 10 is used with the portion inside the speed increaser housing member 23 that is in communication with the circulation conduit 106 located at the lowermost position in the vertical direction. Accordingly, gravitational force stores the oil O inside the speed increaser housing member 23 at the location that is in communication with the circulation conduit 106.

When the pump 101 is driven, the oil O sequentially flows through the circulation conduit 106, the accommodation portion 103, and the supply conduit 105. The oil O is then supplied to the inside of the ring member 62.

The operation of the speed increaser 60 and the centrifugal compressor 10 in the present embodiment will now be described.

When the electric motor 13 is driven and the rollers 71 are rotated, a thin film of the oil O that is solidified, or an elastohydrodynamic lubrication (EHL) film, forms at the ring contact locations Pa and the shaft contact locations Pb. In other words, a thin film of the oil O exists between the circumferential surface of each roller portion 72 and the inner circumferential portion of the circumferential wall 64. In the same manner, a thin film of the oil O that is solidified exists between the circumferential surface of the high-speed shaft 12 and the circumferential surface of each roller portion 72. The thin film of the solidified oil O between the circumferential surface of the high-speed shaft 12 and the circumferential surface of each roller portion 72 transmits the rotation force of the roller 71 to the high-speed shaft 12 and consequently rotates the high-speed shaft 12. The circumferential wall 64 rotates at the same speed as the low-speed shaft 11, and the rollers 71 each rotate at a higher speed than the low-speed shaft 11. Further, the high-speed shaft 12, which is smaller in diameter than each roller portion 72, is rotated at a higher speed than the roller portion 72. In this manner, the speed increaser 60 rotates the high-speed shaft 12 at a higher speed than the low-speed shaft 11.

As described above, in the traction drive type speed increaser 60, the thin film of the oil O solidified at the contact locations Pa and Pb transmits the rotation force of the low-speed shaft 11 to the high-speed shaft 12. It is desirable that the surface pressure applied by the rollers 71 to the inner surface of the circumferential wall 64 and the circumferential surface of the high-speed shaft 12 be raised to solidify the oil O. The present embodiment includes the non-contact surfaces B1 and B2 to reduce the area of contact between each roller portion 72 and the circumferential surface of the high-speed shaft 12. This raises the surface pressure in contrast with when the roller portions 72 do not include the non-contact surfaces B1 and B2. Thus, the oil O easily solidifies at the contact locations Pa and Pb.

When the entire roller portion 72 is shortened in dimension in the axial direction Z, the point of pivot when the high-speed shaft 12 tilts will become closer to the second flange 16. This will increase the movement amount of the projected portion 18 when the high-speed shaft 12 tilts and cause the impeller 52 to easily come into contact with the impeller housing member 50.

In contrast, the roller portion 72 in the present embodiment includes the non-contact surfaces B1 and B2 to reduce the area of contact without decreasing the dimension in the axial direction Z. This increases the surface pressure and limits contact with the impeller 52 when the high-speed shaft 12 tilts.

Like the comparative example shown in FIG. 5, in the rollers 71 that each include the first non-contact surface B1 and the second non-contact surface B2, when the center position CP11 of the contact surface A in the axial direction Z coincides with the center position CP12 of the roller 71 (roller portion 72) in the axial direction Z, the first non-contact surface B1 will have the same area as the second non-contact surface B2. As a result, the first gap C11 will have the same size as the second gap C12.

In contrast, like the present embodiment, when the center position CP1 of the contact surface A in the axial direction Z is located closer to the first flange 15 than the center position CP2 of the roller 71 (roller portion 72) in the axial direction Z, the second gap C2 will be larger than the first gap C1. Thus, the oil O will enter the second gap C2 more easily than the first gap C1, and the second flange 16 will be supplied with a greater amount of the oil O than the first flange 15.

In the centrifugal compressor 10, there is a need to prevent contact of the basal end surface 52 a of the impeller 52 with the cover 26. Thus, the back surface region S4 is defined between the basal end surface 52 a of the impeller 52 and the cover 26. The fluid compressed by the impeller 52 enters the back surface region S4. The compressed fluid pushes the impeller 52 toward the suction port 50 a. This produces a thrust force applied to the high-speed shaft 12 acting from the speed increaser chamber S2 toward the impeller chamber S3. The thrust force pushes the second flange 16 against the second end surface 72 b of each roller portion 72. Thus, the second flange 16 generates heat and wears more easily than the first flange 15. Nevertheless, the oil O is easily supplied to the second flange 16. This reduces wear of the second flange 16.

Further, friction generates heat at the contact locations Pa and Pb. Thus, heat is also generated at each shaft contact portion Pb. When the center position CP1 of the contact surface A in the axial direction Z is located as close as possible to the first flange 15, less heat is transmitted from the shaft contact portion Pb to the second flange 16. This reduces the heat transferred to the second flange 16 where there is a tendency of wear to occur. Thus, wear of the second flange 16 is further limited.

The present embodiment has the advantages described below.

(1) The center position CP1 of the contact surface A in the axial direction Z is located closer to the first flange 15 than the center position CP2 of each roller 71 (roller portion 72) in the axial direction Z. Thus, the second gap C2 is larger than the first gap C1, and the oil O is easily supplied to the second flange 16 where heat is generated more easily than the first flange 15. This limits wear of the second flange 16. This also limits the formation of gaps between the second flange 16 and the second end surface 72 b. Thus, movement of the high-speed shaft 12 in the axial direction and tilting of the high-speed shaft 12 are limited since gaps do not form between the second flange 16 and the second end surface 72 b. Accordingly, the high-speed shaft 12 is stably supported.

(2) The contact surface A is located closer to the first flange 15 than the second flange 16. This reduces the transmission of the heat generated at the shaft contact portion Pb to the second flange 16 and further limits wear of the second flange 16.

(3) The non-contact surfaces B1 and B2 obtain the surface pressure for solidifying the oil O without shortening the dimension of each roller portion 72 in the axial direction Z. This limits contact of the impeller 52 with the inner surface of the impeller housing member 50 that would be caused by shortening the dimension of the entire roller portion 72 in the axial direction Z.

(4) In the centrifugal compressor 10 that includes the speed increaser 60, there are many factors that may tilt the high-speed shaft 12. Nevertheless, the high-speed shaft 12 is stably supported because the dimension of the contact surface A in the axial direction Z is not overly shortened.

(5) The second dimension L2 is longer than the first dimension L1. This increases the exposed area of the second flange 16 in the second gap C2. Thus, the second flange 16 easily comes into contact with the oil O and wear of the second flange 16 is further limited. This further stably supports the high-speed shaft 12.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

As shown in FIG. 6, when increasing the second dimension of the second flange 16 may be increased so that the second end surface 72 b opposes the second flange 16.

The first dimension L1 and the second dimension L2 may be the same. In this case, as shown in FIG. 7, in the axial direction Z, the dimension from the boundary P1 of the first non-contact surface B1 and the contact surface A to the boundary P2 of the first non-contact surface B1 and the first end surface 72 a is referred to as the third dimension L3, the dimension from the boundary P3 of the second non-contact surface B2 and the contact surface A to the boundary P4 of the second non-contact surface B2 and the second end surface 72 b is referred to as the fourth dimension L4, and the fourth dimension L4 is set to be longer than the third dimension L3. This results in the second gap C2 being larger than the first gap C1. Thus, the second flange 16 is easily supplied with the oil O. The third dimension L3 is the dimension from the boundary P1 to the first end surface 72 a in the axial direction Z, and the fourth dimension L4 is the dimension from the boundary P3 to the second end surface 72 b in the axial direction Z.

The non-contact surfaces B1 and B2 do not have to be curved surfaces (surfaces arcuate in cross section) and may be tapered surfaces extending straight from each edge of the contact surface A to the corresponding end surfaces 72 a and 72 b.

The pump does not have to be incorporated in the centrifugal compressor 10 and may be an external pump.

The rollers 71 may be changed in number as long as there is more than one. For example, the number of the rollers 71 may be four or five.

The speed increaser 60 may use a wedge effect. In this case, at least one of the rollers is a movable roller moved by the rotation of the ring member 62.

The centrifugal compressor 10 may be applied to any subject, and the subject compressed by the centrifugal compressor 10 may be any fluid. For example, the centrifugal compressor 10 may be used in an air conditioner, and the fluid that is subject to compression may be a refrigerant. Further, the centrifugal compressor 10 does not have to be installed in a vehicle and may be installed in any subject.

The first flange 15 and the second flange 16 may be changed in form. For example, the first flange 15 and the second flange 16 may be hexagonal or tetragonal.

The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

1. A centrifugal compressor comprising: a ring member including a circumferential wall, wherein the ring member is configured to rotate when a low-speed shaft rotates; a high-speed shaft located at an inner side of the circumferential wall; a plurality of rollers located between the circumferential wall and the high-speed shaft, wherein the rollers are configured to contact the circumferential wall and the high-speed shaft by means of oil; an impeller configured to rotate integrally with the high-speed shaft; a speed increaser housing member that accommodates the ring member, the rollers, and part of the high-speed shaft; and an impeller housing member that accommodates the impeller, wherein: the rollers each include a circumferential surface, a first end surface, and a second end surface, wherein the first end surface and the second end surface are defined by two end surfaces in an axial direction of the roller; the high-speed shaft includes a first flange opposed to the first end surface of each of the rollers, and a second flange opposed to the second end surface of each of the rollers and located farther from the impeller than the first flange in the axial direction of the high-speed shaft; the circumferential surface of each of the rollers includes a contact surface that contacts a portion in a circumferential surface of the high-speed shaft between the first flange and the second flange, a first non-contact surface defined by a portion of the circumferential surface extending from an edge of the contact surface to the first end surface and spaced apart from the circumferential surface of the high-speed shaft, and a second non-contact surface defined by a portion of the circumferential surface extending from an edge of the contact surface to the second end surface and spaced apart from the circumferential surface of the high-speed shaft; and the contact surface includes a center position located closer to the first flange than a center position of each of the rollers in an axial direction of each of the rollers.
 2. The centrifugal compressor according to claim 1, wherein a dimension in a radial direction of each of the rollers from a boundary of the first non-contact surface and the contact surface to a boundary of the first non-contact surface and the first end surface is referred to as a first dimension, a dimension in the radial direction of each of the rollers from a boundary of the second non-contact surface and the contact surface to a boundary of the second non-contact surface and the second end surface is referred to as a second dimension, and the second dimension is longer than the first dimension.
 3. The centrifugal compressor according to claim 1, wherein a dimension in the axial direction of each of the rollers from a boundary of the first non-contact surface and the contact surface to the first end surface is referred to as a third dimension, a dimension in the axial direction of each of the rollers from a boundary of the second non-contact surface and the contact surface to the second end surface is referred to as a fourth dimension, and the fourth dimension is longer than the third dimension.
 4. The centrifugal force according to claim 1, wherein a gap between the first non-contact surface and the circumferential surface of the high-speed shaft defines a first gap, a gap between the second non-contact surface and the circumferential surface of the high-speed shaft defines a second gap, and the second gap is larger than the first gap. 